Abstract: A circuit for generating a trigger blanking voltage for use in the analysis of the ignition voltage waveform of an internal combustion engine which includes a trigger controlled monostable multivibrator furnishing a speed dependent blanking pulse, the width of which is made a function of speed using a capacitor charging circuit coupled to the output of the monostable with feedback of the capacitor voltage to an external circuit determining the duration of the unstable state of the monostable.

Abstract: An engine analyzer for examining the firing voltage curves of spark plugs in internal combustion engines in which two leads are taken from a tap on the high voltage side of the ignition coil with one lead provided to an amplitude discriminator for checking the trailing edge of the portion of the voltage curve referred to as the starting voltage line and the second to an amplitude discriminator for examining what is referred to as the combustion voltage line, with the discriminator outputs provided to a logic circuit which by properly combining the two discriminator outputs gives an indication of proper or improper firing and the type of malfunction present when improper firing occurs.